nixos/tools: generate an xserver config

The desktop configuration won't enable xserver.
If there's multiple desktops enabled they will now evaluate properly.

nixos/modules/installer/tools/tools.nix

@@ -36,6 +36,7 @@ let
     path = lib.optionals (lib.elem "btrfs" config.boot.supportedFilesystems) [ pkgs.btrfs-progs ];
     perl = "${pkgs.perl}/bin/perl -I${pkgs.perlPackages.FileSlurp}/${pkgs.perl.libPrefix}";
     inherit (config.system.nixos-generate-config) configuration desktopConfiguration;
+    xserverEnabled = config.services.xserver.enable;
   };
 
   nixos-option =
@@ -136,6 +137,8 @@ in
         #   keyMap = "us";
         # };
 
+      $xserverConfig
+
       $desktopConfiguration
         # Configure keymap in X11
         # services.xserver.layout = "us";